I've just found something that does pretty much what I want but with mod_perl. For an example, see 13.5 in the following chapter (warning: link is a PDF)
http://www.modperlcookbook.org/chapters/ch13.pdf I thought that I might be able to control the flow from within the access hook! Anyone know if there is a similar method as "set_handlers" in the perl example? Cheers! Ben